In data storage systems, data storage density is always increasing in response to market demand for increased data storage. Each new generation of storage devices increases storage density over previous generations of storage devices, and often in more compact form factors. For example, current enterprise 3.5″ hard disk drives are presently available in 2 TB and 3 TB capacities, while 2.5″ hard disk drives are presently available in 1 TB capacities. Additionally, storage subsystems are being designed to store increasing numbers of storage devices. For example, commercial storage systems are currently available that can store up to 60 storage devices in a 4 rack unit high (4U) rackmountable enclosure.
Traditionally, rackmountable storage enclosures utilize front access, where each storage device is individually mounted to a sled and is inserted or removed from the storage enclosure front. For example, conventional storage enclosures of this arrangement could mount 12 3.5″ storage devices in a 2U enclosure, 16 3.5″ storage devices in a 3U enclosure, or 25 2.5″ storage devices in a 2U enclosure.
High-density storage systems include relatively large numbers of storage devices. In one approach of high-density storage systems, density has been increased by allowing multiple storage devices to be mounted on each front-accessible sled. In some cases, the sleds are wider than a single storage device, sometimes up to the total internal width of a rackmountable shelf. In other cases, the sleds are deeper. In most cases, the storage devices are usually accessed through the top of a sled, after the sled has been pulled out from the front of the storage enclosure. Some high-density storage systems arrange storage devices on both sides of a drawer, where some storage devices of the same drawer are accessed from the left side, and other storage devices are accessed from the right side.
It has been found in recent years that increased numbers of storage devices can be mounted in a single high density storage system by utilizing a “tombstone” storage device mounting approach. A “tombstone” storage system mounts all storage devices vertically on-end in an array of rows and columns, where top access is required for all storage devices. In order to access a storage device in a “tombstone” system, a drawer mounting storage devices of the high-density storage system is usually slid forward on rails. The drawer must be slid forward far enough so that a top cover exposing all storage devices may be removed. A user or system administrator then stands over the top of the drawer and performs any necessary maintenance operation with the storage devices. Although the “tombstone” approach is very space efficient and can mount a large number of storage devices, it has several disadvantages. First, “tombstone” high density storage systems are usually quite heavy and difficult for one or two people to install. Strong slides and mounting structures are required so the entire drawer may be entirely slid forward. Second, “tombstone” storage systems require top access. In some cases, this requires a ladder or other device so that a person can get over the top of the enclosure and service the storage enclosure accordingly. Third, when the storage device drawer is slid forward, the entire weight of the drawer is forward of the rack rails of the rack the system is mounted within, possibly making the entire rack unstable and able to tip over.